[Forced expiration. Various current concepts, 50 years after Robert Tiffeneau]

One hundred and fifty years after the original description of spirometry by Hutchinson and 50 years after the definition of his famous ratio by Tiffeneau, a certain number of physiological advances have enabled a better understanding of the determinants of the forced expired manoeuvre and to mitigate some of its inconveniences. This review focuses on three of these advances. The first is the influence of an inspiratory manoeuvre which precedes a forced expiration, on the expiratory flow. This influence is probably a consequence of viscoelastic phenomena and impose some strains on standardisation in current practice. The second is the possibility of detecting in a reproducible and simple fashion, without the need for co-operation on the part of the subject, a limitation in expiratory flow by the application of a negative expiratory pressure at the opening of the airways (NEP for negative expiratory pressure). The third is the possibility to verify in a simple fashion the quality of the expiratory performance achieved by the patient and thus to detect an insufficient effort in the force of a falling expiratory flow.